Material condensing in the corona and appearing to rain down into the chromosphere as observed in H-alpha at the solar limb. Earth impacting CMEs can result in significant geomagnetic storms. Large and fast CMEs can approach densities of 10 16 g and velocities of 2000 km/s. CMEs vary widely in structure, density, and velocity. CMEs are often, but not always, associated with erupting prominences, disappearing solar filaments, and/or flares. Coronal loops represent ”closed” magnetic topology.Īn outflow of plasma from or through the solar corona. The solar wind emanating from these holes is characteristically high in velocity and low in density.Ī typical structure of enhanced corona observed in EUV lines and soft x-rays. Transequatorial coronal holes are the source of many recurrent geomagnetic disturbances since their lifetimes are months to years. Coronal holes are visible in several wavelengths. Coronal holes are largest and most stable at or near the solar poles, and are a source of high-speed solar wind. A simple lens focuses the Sun onto an occulting disk that prevents the light from the solar disk from proceeding farther along the optical path, effectively providing an artificial eclipse.Īn extended region of the corona, exceptionally low in density and associated with unipolar photospheric regions having ”open” magnetic field topology. In spectroscopy, and in particular the solar Fraunhofer spectrum, a characteristic wavelength of emitted radiation that is partially absorbed by the medium between the source and the observer.Ī descriptive word specifically meaning (1) a probability of ~50% for an M- class x-ray flare (see x-ray flare class) (2) disturbed geomagnetic levels such that 16 10 6 K).Īn optical device that makes it possible to observe the corona at times other than during an eclipse. The index is available back to 1868, and is provided by the Institut du Globe de Paris, France. A daily and half-daily index of geomagnetic activity determined from the k indices scaled at two nearly antipodal stations at invariant magnetic latitude 50 degrees (Hartland, England, and Canberra, Australia).
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